1. Field of the Invention
The present invention relates to an imaging module, particularly a small size imaging module which is to be disposed at a front end portion of an electronic endoscope, and a method of manufacturing imaging module.
2. Description of the Related Art
In recent years, an endoscope for observing an inside of a body by inserting a long and slender inserting section into the body has been widely used. An electronic endoscope is an example of such endoscope. The electronic endoscope has a built-in imaging module which is provided with a solid state imaging device such as a charge coupled device (CCD) at a front-end hard portion.
The front-end hard portion is expected to be shortened, and have a thin diameter in order to ease patient's pain. Therefore, a size reduction of the solid state imaging device, and size reduction of the imaging module after the solid state imaging device is mounted becomes important. Regarding the size reduction of the imaging module, it is desired that an area of the imaging module viewed from the front side is not increased as far as possible, as compared to an area of the solid state imaging device.
For example, in Japanese Patent Application Laid-open Publication No. Hei 10-192236, such electronic endoscope has been proposed. FIG. 7 shows a schematic structure of a front-end portion of the electronic endoscope in the Japanese Patent Application Laid-open Publication No. Hei 10-192236. Here, an inner lead 22 of a flexible substrate 20 is attached by bonding to a pad portion provided on a solid state imaging device 10 directed similarly as a light receiving surface 11. The inner lead 22 is arranged upon bending to face backward of the light receiving surface 11 along a side surface of the solid state imaging device 10. Moreover, an electrical insulating member 70 or an electrical insulating member 80 in a sheet form is applied to a surface of the inner lead 22, along the solid state imaging device 10, excluding a portion which is attached by bonding to the pad portion.
Accordingly, an electrical insulation between the side surface of the solid state imaging device 10 and the inner lead 22 is secured, and besides, an overall size of an assembly of a unit of the solid state imaging device 10 and the flexible substrate 20 is made small.
In a small size imaging unit which is to be disposed at the front end portion of an endoscope, it is desirable to reduce as much as possible a radius of curvature of a bent portion, and an amount of resin potting. However, in a structure according to the conventional technology, when the inner lead 22 is to be bent, from a point of view of securing mechanical strength and a point of view of securing insulation with the solid state imaging device, it is necessary to bend to a radius of curvature of certain magnitude. Moreover, practically, it is necessary to reinforce the mechanical strength of the bending portion of the inner lead 22 by potting the resin. In this manner, in the structure according to the conventional technology, it is difficult to secure high mechanical strength while maintaining a thin diameter.